The present invention relates to a magnetic head.
Heretofore, a magnetic head in which a magnetoresistance effect element which alters its resistivity when a magnetic field is impressed on the ferromagnetic body is utilized has been used in ways such way as shown in FIGS. 1A and 1B.
In the magnetic head shown in FIG. 1A, the magnetoresistance effect element (2) composed of a ferromagnetic thin plate abuts or approaches, in the vertical Y direction, a recording medium (1) (e.g., magnetic tapes, etc.), and electrodes (3) and (4) are provided at both ends of the magnetoresistance effect element (2) as seen in the direction of its length (Z direction); then, with a constant current flowing across the electrodes (3) and (4), the change in electrical resistance in the Z direction due to the signal field in the Y direction induced by the recording medium (1) is detected as a voltage change across the electrodes (3) and (4). In this instance, the strength of the signal field induced by the recording medium (1) attenuates as an exponential function of the width W in the Y direction of the magnetoresistance effect element (2), and especially when the recorded wave length on the recording medium (1) is short, the attenuation of the signal field in the width direction of the magnetoresistance effect element becomes very large. In order to avert such attenuation, the magnetoresistance effect element (2) can be arranged parallel to the recording medium (1), as shown in FIG. 1(B). Then, the separation loss in the Y direction is reduced to almost zero. The wear due to the sliding contact with the recording medium (1), however, poses a problem, a real problem practical applications, because the magnetoresistance effect element (2) is generally in a thin plate shape.
The resistivity of the magnetoresistance effect element (2) is given by the equation .rho. = .rho..sub.o + .DELTA..rho..sub.max cos.sup.2 .theta., where .theta. is the angle between the direction of the magnetization of the ferromagnetic thin plate and the direction of current. Accordingly, the ratio .DELTA..rho./.DELTA..rho..sub.max of the change in the resistivity to the maximum change in the resistivity when plotted on a graph against the impressed magnetic field H produces a noticeable nonlinearilty as shown in FIG. 2. It is, therefore, necessary to set the operation point at P in FIG. 2 by applying a bias field for the purpose of avoiding this nonlinearity and widening the dynamic range so far as possible.
Thus, in the magnetoresistance effect element (2), it is necessary from the operation standpoint to achieve a bigger rate of change of resistivity relative to the magnetic field in the range of magnetization rotation of the ferromagnetic material. When the direction of magnetization in the magnetoresistance effect element (2) is rotated by the signal field, the relationship between the ratio [d(.DELTA..rho.)/d.theta.] of the rate of change of resistivity to the rate of change of rotation angle and the rotation angle .theta. is shown in FIG. 3, and the ratio [d(.DELTA..rho.)/d.theta.] is a maximum at .theta.= 45.degree.. That is to say, it is in this state that the sensitivity of the magnetoresistance effect element (2) to the magnetic field is the highest, and moreover, the operation point is set in the widest dynamic range. The change of resistivity in FIG. 3 is normalized by the value .DELTA..rho..sub.max of maximum change of resistivity. For this purpose, the bias field is impressed in a direction at a right angle to the Z axis direction, which is the current direction in the conventional devices. In this state, the highly magnetic thin plate used as the magnetoresistance effect element (2) should desirably be oriented having uniaxial anisotropy to avoid hysteresis. Accordingly, in the conventional devices, predominant magnetization axis is oriented in the Z axis direction; then, the signal field is impressed in the Y axis or X axis direction, being respectively at right angles thereto, and the bias field is applied in the same direction as that of the signal field. With this arrangement, however, some effect, however small, exerted by the bias field on the recording medium (1) is unavoidable.